If you want to study gene expression in log phase, then you want to rapidly freeze the bacteria, not dramatically change the environment by stopping growth! You will most certainly dramatically change expression levels of genes by keeping the cells viable and inhibiting growth. I'd suggest a quench in liquid nitrogen or dry ice/ethanol to rapidly freeze them, followed by rapid extraction of RNA with Trizol.

If you want to study gene expression in log phase, then you want to rapidly freeze the bacteria, not dramatically change the environment by stopping growth! You will most certainly dramatically change expression levels of genes by keeping the cells viable and inhibiting growth. I'd suggest a quench in liquid nitrogen or dry ice/ethanol to rapidly freeze them, followed by rapid extraction of RNA with Trizol.

Its very simple: as soon as you change the conditions (give the bacteria stress) you will induce other genes and thus get other geneproducts (other mRNA). So you need to "stopt" your bacteria as fast as possible (with as less stress as possible).So "stopping" the bacteria with liquid nitrogen is an obtion.

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